This invention relates to a roof jack assembly for a furnace, and, more particularly, to a telescoping roof jack assembly which cannot be pulled apart.
Sealed combustion forced air furnaces conventionally use of roof jack assembly for supplying combustion air and for exhausting flue gases. The roof jack assembly extends upwardly from the furnace through the roof of the dwelling and includes an inner tube for exhausting flue gases and an outer tube for supplying outside air for combustion.
Sealed combustion furnaces are commonly used in mobile homes or manufactured housing. Mobile homes are usually provided with a very tight, sealed construction, and all of the air for combustion in the furnace must be obtained from outside the home.
Conventional roof jacks consist of two concentric tubes. The inner tube provides a passage for flue gases to the outside, and the outer tube provides a path for combustion air from the outside to the furnace burner. The upper ends of the inner and outer tubes terminate above the roof line of the home and are protected by rain caps.
Manufactured homes are built with wide variations of roof heights and variations in attic depts and ceiling heights above the furnace. Accordingly, roof jacks must either have a telescoping feature, or the tubes must be long enough to accommodate the widest variation and then be cut to length at the time of installation. The disadvantage with the latter procedure is that this is basically a cut-and-try installation for each particular home, and proper fit is totally dependent on the care and expertise of the installer.
The telescoping feature allows flexibility in the installation. However, even with a telescoping jack, the wide variations in roof heights and attic cavity depths require the availability of several different lengths of telescoping roof jacks. When too short a telescoping assembly is used, the telescoping tubes can be pulled apart. Further, the outer and inner tubes generally telescope independently of each other, which raises the possibility that one or the other of the tubes might not be securely attached to the furnace.